Geographic Range

The grey reef shark occupies a widespread range from the eastern Pacific Ocean (Costa Rica) through the western Pacific and Indian Oceans, and in the Red Sea. Grey reef sharks are most commonly encountered off the islands of Tahiti, Micronesia, Fiji, Papua New Guinea, and Malaysia. (Murphy, 1993)

Physical Description

Grey reef sharks have sleek, fusiform bodies that are unmistakable for anything but a shark. Key physical features include the anal fin, five gill slits, and a mouth positioned behind the eyes and underneath the snout. Additionally, grey reef sharks appear grey from a distance, but show a bronze tint when viewed up close. They have a white underside and are distinguished by a broad black band on the edge of the tail and black markings on the tips of the pectoral fins. The dorsal fin is either grey or tipped white. They have a long, broadly rounded snout and round eyes. They are lacking an interdorsal fin. (Murphy, 1993)

Males grow up to 255 cm in length, and are 130-145 cm long at maturity, while females are a bit smaller, maturing at 120-135 cm, with a record length of 172 cm. Males are distinguished by the elongate mating claspers on their pelvic fins. The maximum published weight for an individual of this species is 33.7 kg, but large males may be heavier. (Compagno, 1984; Fishbase, 2003; Godknecht, 2004; Murphy, 1993)

Grey reef sharks can be easily mistaken for similar species of requiem sharks. The blacktip shark (Carcharhinus limbatus) and the blacktip reef shark (Carcharhinus melanopterus) can be distinguised by a black tip on the dorsal fin, while the dorsal fin of C. amblyrhynchos is white or grey. Similarly, the silvertip shark (Carcharhinus albimarginatus) has white tips on its pectoral and caudal fins, while C. amblyrhynchos does not. (Godknecht, 2004)

Development

The species is viviparous, meaning that its embryos are connected to a placenta-like yolk sac, and the young are born alive and free-swimming, not in an egg. Females give birth to live young, usually sized between 46 and 60 cm. Males mature at a length of 130-145 cm, and females at 122-137 cm. (Perrine, 1995)

Reproduction

Carcharhinus amblyrhynchos mate through internal fertilization. When a female is ready to mate, she will give off behavioral and chemical cues (pheromones). When the male senses these cues, he pursues her and seizes her with his teeth, which can actually cause serious wounds. Females have thicker skin on their backs than males do, probably to protect them from male biting.

We have no information on the seasonality of mating in this species, or how many mates males or females have when breeding. (Compagno, 1984; Perrine, 1995)

As in all sharks, male gray reef sharks have paired reproductive structures called "claspers," located between the pelvic fins. A groove in each clasper directs sperm into the female's cloaca during mating. Sperm may fertilize the egg then, or may be stored until an egg is released.

Females produce 1-6 offspring at a time, and the embryos gestate for about 12 months before birth.

Behavior

Gray reef sharks are social, maintaining daytime schools, but becoming more active nocturnally. This species usually swims slowly (about 0.5 mph), seemingly inactive. However, because of its extremely sensitive perception channels, it is always constantly aware of its surroundings. When food is near or tasted, this species will speed up and become more active very quickly. Additionally, when it feels the vibrations of a fish dying it becomes highly aggressive. These sharks can be territorial. They have a very distinct agonistic display that they make to other sharks, and sometimes to human divers. A displaying shark will arch its back, point its pectoral fins completely downwards, and swing its head laterally in a slow pendulum-like motion as it swims. (Murphy, 1993; Perrine, 1995)

Home Range

No home range size has been specified. However, C. amblyrhynchos have been known to act aggressively towards other predatory sharks of similar size.

Communication and Perception

Carcharhinus amblyrhynchos perceives its environment very much through its excellent sense of smell. It can detect very low concentrations of blood by swinging its head side to side and using both nostrils to sample the water. All of its senses are acute. Its vision is sensitive to blue-green and low light because there are many rod cells in the retina. These sharks are generally thought to be far-sighted, but they can hunt by starlight. Grey reef sharks "hear" by detecting sounds through vibrations using sensory pits called the lateral line system. They have inner-ear semicircular canals used for balance, motion, and vibration. Most unique is its electromagnetic sense. This is facilitated by pores known as "ampullae of Lorenzini" that are concentrated around the snout. As sharks move through the earth's magnetic field, they create an electric field. By sensing this field, they can detect the strength and direction of it. This is the grey reef shark's navigation system.

These sharks communicate with other sharks visually (see the Behavior section for details of their territorial defense display) and by touch (see Mating Systems). (Perrine, 1995)

Food Habits

The primary diet of C. amblyrhynchos is bony reef fishes less than 30 cm long. It also eats squid, octopi, crabs, lobsters, and shrimp. These sharks catch their food with their jaws and sharp teeth. When hunting, grey reef sharks have been observed swimming at speeds of up to 30 mph (48 km/h). (Compagno, 1984)

Ecosystem Roles

Grey reef sharks are usually the top predators on coral reefs, controlling the fish populations under them.

Economic Importance for Humans: Positive

Since grey reef sharks are generally a harmless and inquisitive species, studies are conducted on them quite easily. Ecotourism in the form of "shark diving" has also recently blossomed into a large industry. (Murphy, 1993)

Economic Importance for Humans: Negative

Although usually considered harmless, C. amblyrhynchos may occasionally bite humans. The bites are serious, but rarely fatal. Accidents most often occur during spearfishing, when the sharks become aggressive in the presence of food. Careless divers who corner the animal in a reef canyon may also be attacked in self-defense. Additionally, there are areas of eastern Micronesia, particularly the Marshall Islands, where these sharks have a reputation for being aggressive toward humans.

Negative Impacts

injures humans

bites or stings

Conservation Status

While the grey reef shark has not been identified as endangered as of yet, depletion of the species has been noticed around the Maldive Islands, and may be occurring in other parts of its range. There are several aspects of the biology and behavior of this species that make it particularly vulnerable to over-fishing. It is found relatively near shore, individuals tend to stay in one area, and they gather in predictable locations, making them easier to catch. Females matures relatively slowly, and have small litters, which means slower population growth compared to other large fish. (Fishbase, 2003; Godknecht, 2004)

Glossary

body of water between the southern ocean (above 60 degrees south latitude), Australia, Asia, and the western hemisphere. This is the world's largest ocean, covering about 28% of the world's surface.

acoustic

uses sound to communicate

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

coastal

the nearshore aquatic habitats near a coast, or shoreline.

diurnal

active during the day, 2. lasting for one day.

ecotourism

humans benefit economically by promoting tourism that focuses on the appreciation of natural areas or animals. Ecotourism implies that there are existing programs that profit from the appreciation of natural areas or animals.

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

electric

uses electric signals to communicate

fertilization

union of egg and spermatozoan

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

internal fertilization

fertilization takes place within the female's body

magnetic

(as perception channel keyword). This animal has a special ability to detect the Earth's magnetic fields.

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

nocturnal

active during the night

pelagic

An aquatic biome consisting of the open ocean, far from land, does not include sea bottom (benthic zone).

pheromones

chemicals released into air or water that are detected by and responded to by other animals of the same species

piscivore

an animal that mainly eats fish

reef

structure produced by the calcium carbonate skeletons of coral polyps (Class Anthozoa). Coral reefs are found in warm, shallow oceans with low nutrient availability. They form the basis for rich communities of other invertebrates, plants, fish, and protists. The polyps live only on the reef surface. Because they depend on symbiotic photosynthetic algae, zooxanthellae, they cannot live where light does not penetrate.

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

social

associates with others of its species; forms social groups.

sperm-storing

mature spermatozoa are stored by females following copulation. Male sperm storage also occurs, as sperm are retained in the male epididymes (in mammals) for a period that can, in some cases, extend over several weeks or more, but here we use the term to refer only to sperm storage by females.

tactile

uses touch to communicate

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

vibrations

movements of a hard surface that are produced by animals as signals to others

visual

uses sight to communicate

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

Disclaimer:
The Animal Diversity Web is an educational resource written largely by and for college students. ADW doesn't cover all species in the world, nor does it include all the latest scientific information about organisms we describe. Though we edit our accounts for accuracy, we cannot guarantee all information in those accounts. While ADW staff and contributors provide references to books and websites that we believe are reputable, we cannot necessarily endorse the contents of references beyond our control.

This material is based upon work supported by the
National Science Foundation
Grants DRL 0089283, DRL 0628151, DUE 0633095, DRL 0918590, and DUE 1122742. Additional support has come from the Marisla Foundation, UM College of Literature, Science, and the Arts, Museum of Zoology, and Information and Technology Services.